1. Field of the Invention
This invention relates to a method of manufacturing a thin film magnetic head usable for a magnetic recording and reading device such as a magnetic disk device, particularly to a method of manufacturing a thin film magnetic head with an inductive type thin film magnetic head for writing having a first magnetic member including a first pole portion and a first yoke part, a second magnetic member including a second pole portion constituting an air bearing surface (often abbreviated to "ABS") opposing to the first pole portion via a write gap film and to a magnetic recording medium as well as the first pole portion and a second yoke part magnetically connected to the first yoke part in the position apart from the air bearing surface, and a thin film coil including the part surrounded by the first and second magnetic members.
2. Related Art Statement
As a thin film magnetic head usable for a magnetic disk device constituting a memory device in a computer, a composite type thin film magnetic head has been mainly used in which an inductive type thin film magnetic head is employed as a writing element and a magnetoresistive effective type thin film magnetic head is employed as a reading element.
For realizing a high density recording using such a thin film magnetic head, data capacity (surface recording density) to be stored in a unit area of a magnetic disk has to be increased. The surface recording density firstly depends on a performance of a writing element. The surface recording density can be enhanced by shortening the gap length of the writing pole in the writing element. However, the shortening of the gap length is restricted in itself because it causes the magnetic flux in the writing pole to be decreased.
The other means to develop the surface recording density is to increase data track number able to be recorded in a magnetic disk. The track number capable of being recorded in a magnetic disk is represented as TPI (track per inch). The TPI of the writing element can be enhanced by minifying the head size to define the width of the data track. The head size is usually denominated as the track width of the head.
The narrowing the track width is disclosed in various publicly known documents. For example, the specifications of U.S. Pat. No. 5,438,747 and U.S. Pat. No. 5,452,164 disclose the method that a first pole portion is etched by ion beam milling with a second pole portion obtained by photolithography as a mask so that its track width can be equal to the track width of the second pole portion.
Moreover, the specification of U.S. Pat. No. 5,285,340 disclose the following method:
After a first magnetic yoke layer (first yoke part) is formed, a photoresist layer is stuck and an opening is provided to form, on the photoresist layer, a magnetic pole end assembly composed of a first pole portion, a write gap film and a second pole portion into a desired pattern. Then, after the magnetic pole end assembly is formed in the opening, the part of the photoresist layer positioning in the front of the magnetic pole end assembly is removed. Thereafter, a thin film coil, an insulating film, etc. are formed by a conventional method and a second magnetic yoke layer (second yoke part) is formed.
The above technique is to define the track width by using the mask patterned by the photolithography. However, the narrower the track width of the writing pole portion is, the larger the aspect ratio (ratio "t/w" of thickness "t" to width "w") of the magnetic film constituting the writing pole portion is. In the case of defining the track width by using the mask patterned by the photolithography, if the aspect ratio of the magnetic film is larger, inevitably, the ratio of the height of the resist frame to the frame space to define the track width is larger, so that the magnetic film is unlikely to be smoothly plateformed and the magnetic characteristics of the writing pole portion become unstable to degrade the recording performance.
Moreover, the thin film magnetic head has the highly rising coil insulating film to support the thin film coil. Thus, in the process of forming the second yoke part by the photolithography, the photoresist is stuck thickly on the step when the photoresist layer is formed. Consequently, the pattern of the second pole portion formed on the downside of the step has to be patterned through the thick photoresist layer and the aspect ratio (the ratio of the height to the width of the resist) is remarkably large, resulting in the difficulty of narrowing the track width. From the above reasons, in the past, the track width of about 0.8 .mu.m could be obtained in its limit.